1. Field of the Invention
The present invention relates to a loudspeaker diaphragm.
2. Description of the Related Art
In general, it is desirable for a loudspeaker diaphragm to have a high specific modulus E/ρ (E is modulus of elasticity; ρ is density) for broadening the piston motion region and to have a high internal loss for smoothing the frequency characteristic.
Hitherto, for enhancing the modulus of elasticity E, materials obtained by loading a polypropylene material having a comparatively high internal loss with high-elasticity fibers or filler have been frequently used in injection molding and sheet molding.
However, since the specific gravity of the molding material increases with an increase in the addition amount of the fibers or filler, enhancement of the specific modulus is restrained. In addition, injection molding is accompanied by a lowering in resin flow length, making it difficult to achieve thin-wall molding. Thus, there has been a limit to enhancement of both the specific modulus and the internal loss.
In view of the above, the present applicant, in Japanese Patent No. 2670365, has proposed a loudspeaker diaphragm produced by a method in which a thermoplastic resin composed mainly of a polyolefin composition produced by multistage polymerization and containing an ultrahigh molecular weight polyolefin having a limiting viscosity of 10 to 40 dl/g as measured in a decalin solution at 135° C. and a low molecular weight or high molecular weight polyolefin having a limiting viscosity of 0.1 to 5 dl/g as measured in a decalin solution at 135° C. is injection molded, and the ultrahigh molecular weight polyolefin is oriented radially.
This loudspeaker diaphragm has successfully realized a lower weight and a higher modulus of elasticity, as compared with the case of using the above-mentioned polypropylene composite material.